1. Field of the Invention
The present invention relates to a piezoelectric vibrator, an oscillator, an electronic apparatus, and a radio-controlled timepiece.
2. Description of the Related Art
In recent years, piezoelectric vibrators using crystal or the like have been used in mobile phones or portable information terminals as a time source, a control signal timing source, a reference signal source, and the like. Various piezoelectric vibrators are available as such kinds of piezoelectric vibrators, and a piezoelectric vibrator in which a so-called tuning fork-type piezoelectric vibrating reed is sealed in a package is also known as one of the piezoelectric vibrators.
A tuning-fork-type piezoelectric vibrating reed is a thin plate-like crystal reed which includes a pair of vibrating arms arranged in a line in a width direction thereof and a base portion that integrally fixes base end sides in the longitudinal direction of the pair of vibrating arms. A pair of excitation electrodes is formed on both the upper and lower surfaces of each of the vibrating arms of the piezoelectric vibrating reed with a predetermined gap therebetween. Moreover, a pair of mount electrodes is formed on both the upper and lower surfaces of the base portion and electrically connected to a pair of excitation electrodes through a pair of extraction electrodes. On the other hand, bumps made of gold or the like are formed on the inner electrodes of the package.
The mount electrodes of the piezoelectric vibrating reed are mounted on the inner electrodes of the package, whereby a piezoelectric vibrator is formed. Specifically, the piezoelectric vibrating reed is mounted in the package by a so-called flip-chip bonding method in which the mount electrodes of the piezoelectric vibrating reed are pressed against the bumps on the inner electrodes to cause ultrasonic vibration, whereby the mount electrodes and the bumps are ultrasonically bonded to each other.
However, when the piezoelectric vibrating reed is mounted in the package by the flip-chip bonding method, the mounting strength of the piezoelectric vibrating reed decreases if the number of bumps being bonded is small. Moreover, when an impact load is applied to the piezoelectric vibrator, there is a problem in that the piezoelectric vibrating reed falls off the mounting surface of the package, and accordingly, an oscillation stops. In order to obviate such a problem, a method of increasing the number of bumps to improve the mounting strength of the piezoelectric vibrating reed may be considered.
JP-A-2007-096899 discloses a piezoelectric vibrating reed in which two bumps are formed on each of a pair of connection electrodes (corresponding to the lead-out electrodes of the present invention) in the package along the longitudinal direction of the piezoelectric vibrating reed, and the respective bumps are bonded to pad electrodes (corresponding to the mount electrodes of the present invention). In the piezoelectric vibrating reed disclosed in JP-A-2007-096899, since the piezoelectric vibrating reed is mounted on the package using four bumps in total, even when an impact load is applied to the piezoelectric vibrator, stress resulting from the impact load applied to the bonding portion of the piezoelectric vibrating reed can be distributed to a plurality of bumps. Therefore, the mounting strength of the piezoelectric vibrating reed can be improved.
However, since the piezoelectric vibrating reed disclosed in JP-A-2007-096899 is firmly mounted on the package by means of a plurality of bumps, there is a possibility that, when the piezoelectric vibrating reed is operated, so-called vibration leakage may occur. That is, vibration energy of the piezoelectric vibrating reed may leak to the outside through the plurality of bumps. When vibration energy of the piezoelectric vibrating reed leaks to the outside when vibration leakage occurs, there is a possibility that the energy efficiency of the piezoelectric vibrator will decrease. Moreover, when the piezoelectric vibrator with vibration leakage is mounted on a substrate of an electronic apparatus or the like, since the degree of binding of the piezoelectric vibrator is different in accordance with solid variations in the mounting state such as the amount of solder, there is a problem in that the vibration properties of the piezoelectric vibrator fluctuate.